In an Ethernet network, a ring shape topology of a plurality of repeaters, i.e., Ethernet “switches” or network switches, is arranged by connecting those repeaters in a ring shape. In such a ring shape topology of the repeaters, or the switches, two ports of one switch are respectively connected to ports of two other (i.e., two different) switches, for a ring shape topology of communication path arrangement of the network. Thus, as a result, two communication paths are established between the two switches, one communication path along a clockwise direction of the ring shape network and the other communication path along a counter-clockwise direction, from one (sender) switch to the other (receiver/destination) switch.
More practically, the following situation clarifies the above description. That is, when one switch has at least four ports, among which two ports are ring ports for a ring connection of the subject switches, and the other two ports are normal ports that are respectively connected to two devices (e.g., when one of the two normal ports of a switch 1 is connected to a device A (e.g., ECU X) and one of the two normal ports of a switch 2 is connected to a device B (e.g., ECU Y)), one data communication frame transmitted from the device A reaches the device B in either of the two communication paths described above, because (path A) the transmitted frame from the device A may come in from one normal port of the switch 1 to go out from one ring port of the switch 1 to take a clockwise path to reach the switch 2 and to go out from one normal port to the device B, and (path B) the transmitted frame from the device A may come in from one normal port of the switch 1 to go out from the other ring port of the switch 1 to take a counter-clockwise path to reach the switch 2 and to go out from the same normal port to the device B. In other words, two communication paths, i.e., the path A and the path B, are provided for communication between the two devices A and B.
On the other hand, a patent document, WO 2010-509825, (Patent document 1) discloses an idea of transferring the frame in a predetermined shortest path to the destination, i.e., from one node to the other node.
When the Ethernet network is used to form a ring topology of the devices, one data communication frame may either be sent out to take (i) both of the two paths in the ring topology to reach the destination device or (ii) only one of the two paths in the ring topology to reach the destination device. In either case, the transmission time of one data communication frame is bound/affected by the communication speed of the one path.